Ultrahigh-frequency converter



Sept. 22, 1953 wl-:N YUAN PAN ULTRAHIGH-FREQUENCY CONVERTERl Filed Aug. 1e, 1951 A A INVEN-roR BIEN YuHN PHN Patented Sept. 22, n1953 UNITED STATES S''EN @ENCE ULTRAHIGH-FREQUENCY CONVERTER Wen Yuan Pan, Collingswood, N. J.. assgnor to Radio Corporation of America,v a corporation or` Delaware Applica-tion August 1s, 1951, serial? NQ.,242,1,61

8 Claims. (Cl. 1 2 This invention relates generally' 'G0 frequency to cover a television band such as that nowtentaconverters, and particularly relates to a frequency tively allocated in the frequency range from 470 conversion system including a mixer and an osto 890 mc., the oscillatory energy injected in the cillatio-n generator suitable for use in the ultra y conventional manner on the mixer of a frequency highfrequency (U. H. F.) spectrum. U converter may vary as much as 1000 to 1.

A conventional frequency converter for a It is accordingly the principal object of the U. H; F. band includes a crystal mixer and an present invention to. provide a U. H. F. converter oscillation generator. The mixer has an input system wherein means are provided to maintain circuit tunable over the desired band and an outy the oscillatory energy impressed on the mixer put circuit tuned to a xed intermediate freof the system substantially constant throughout q-uency. The oscillatory wave energy is prefthe tuning range of the oscillator. erably injected between the mixer and its out- A further object of the invention is to provide put circuit to reduce oscillator radiation. It has for effectively shunting the local oscillator of the been found that several: important performance U. H. F. converter system by an oscillator wave characteristics of a U. H'. 'E'. converter depend. L) path having a low impedance which varies Within upon the amount of oscillatory energy impressed very narrow limits over the oscillator tuning on the crystal mixer. These performance charrange and which controls the oscillatory wave acteristics include the undesired oscillator radienergy impressed on Vthe mixer of the converter ation, spurious responses which are caused by system so as to maintain it substantially constant. harmonics generated inthe mixer during the 29 A U. H. F. converter system may comprise a mixing process and the-noise factor. crystal mixer having a resonant input circuit rIfhe undesirable oscillator radiation through eonnec-ted'to one of its electrodes. The resonant the antenna terminals lof a U'. l-I. F.7converter is input circuit is tunable within a predetermined determined by the intermediate frequency, the portion of the U. H. F. spectrum to receive a band width of the radio-frequency input circuit 25 desired modulated carrier wave. Aresonant out#- Uf the mxerand by the amount Of the oscillatory' put circuit tuned to a predetermined intermediate energy impressed on the mixer. It will be obvious frequency is connected to the output electrode of that as the oscillator radiation becomes smaller, the mixer. A local oscillator is provided for inthe smaller the oscillatory energy impressed on j ecting oscillatory energy preferably upon the the' mXeI- 0H the Other hand, the OS-Cllatoly :it output electrode of the mixer to reduce oscilenergy impressed on the mixer should be high lator radiation through the antenna terminals. in order to reduce the conversion loss, thus in- The local oscillator istunable within another porcreasing the mixerelciency. Accordingly the tion ofthe U. H. F. spectrum. oscillatoryenergy impressed on the mixer should In accordance with the present invention, have an optimum value which is of the order of :to means are provided for maintaining the oscil- 500- microwatts provided the mixer is a silicon latory wave energy impressed on the crystal mixer crystal such as the 1-N2i-B type or a germanium substantially constant throughout the tuning crystal of the 1N72 orv Oli-710 type. If the crysrange,` of the local oscillator. This means comta-l is excited: with either too high or too low amprises a capacitor and a resistor connected seplitude oscillatory energy. the converter is also 4o rially between the output electrode of the mixer more susceptible to spurious responses in the and ground. Accordingly, the capacitor and represence of interfering signals. sistor effectively shunt the crystal mixer. The

Furthermore, wide uctuations ofthe oscillacapacitor and resistor have a combined impedtoryenergy impressed on the mixer may cause ance which varies withinr very narrow limits over variations ci the impedance match between the 45 the. oscillator tuning range. The leads which crystal and its input and output circuits. Such connect. the capacitor and resistor between the varia-tions may introduce mismatch between the mixer electrode and ground represent inductance crystal mixer and its radio frequency input cirwhich is added to the impedance of the shunt cuit aswell as between the crystal and its interpath provided by the resistor and capacitor.

mediate frequency output circuit. It will ac- 50 rThus if the shunt path would include only a cording-ly be obvious that the crystal should be capacitor, its capacitance would be series resexcited by the optimum Value 0f the OSCllatOI'Y onant with the inductance of the lead so that energy and that this value should remain subwithin a certain portion of the oscillator range stantially constantA over the entire tuningr range. the oscillator would be effectively short-circuited.

If' the TJ. H. F'. converter is, for example, designed 55 A return path for the direct current flowing through the crystal mixer may include a first inductor forming part of the mixer input circuit and connected between the mixer and ground. A second inductor which functions as a choke may be connected between the mixer output electrode and ground to complete the direct current return path.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which:

Figure l is a circuit diagram of aUcI-I. F. converter embodying the present invention;

Figure 2 is an equivalent circuit diagram of the mixer and oscillator of the converter of Fisure 1; and

Figure 3 is a graph illustrating the rectied current owing through the crystal mixer of the invention and through that of a conventional U. H. F. converter as a function of frequency.

Referring now to the drawing there is illustrated in Figure 1 a U. H. F. converter comprismg an antenna Iii, a crystal mixer Il, a local oscillator i2 and an intermediate frequency ainplier stage i3 as is conventional. The mixer i! preferably 4consists of a crystal rectier such 'as a silicon crystal rectifier of the 1N21B type or a germanium crystal rectiiier of the 1N72 or CK-'710 type. The crystal rectiiier or mixer Il has two electrodes as illustrated; one being in ohmic contact and one in rectifying Contact with the crystal. However, it is immaterial to which electrode the input circuit is connected.

The input circuit of the mixer H includes the antenna it which may, for example, be a dipole and which is connected to a transmission line i5 such as a coaxial line having its outer conductor grounded as shown. A high pass iilter it is connected between the transmission line i5 and the radio-frequency input circuit Vi. The high pass filter IE may be a constant K iilter and comprises two capacitors connected in series and an inductor connected between the junction point of the capacitors and ground.

rThe high pass iilter IS may, for example, reject u the very high frequency television channels 2 to I3.

The radio-frequency input circuit Il may include two series resonant tunable circuits 2li and 2i. Resonant circuit 2i) includes an inductor 22 having an intermediate point connected to the high pass filter I 6 to match the impedance of the lter i5 to that of the resonant circuit 26. The lower terminal of inductor 22 may be grounded as shown. The series resonant circuits Zil and 2| each include a capacitor 23 and M which. may be varied in unison as indicated at 25. The two series resonant circuits 2li, 2i are magnetically coupled through their respective inductors 26 and 21. The inductor 23 of the series resonant circuit 2'I has an intermediate point connected to one of the electrodes of the crystal mixer Il which may be called the input electrode, thereby to match the impedance of the input circuit I1 to that of the mixer Il. The lower terminal of inductor 28 is grounded as shown.

A pair of series resonant lter structures providing a double tuned filter of the type illustrated at El in Figure 1 has been d SClQSed @nfl w an inductor 3i connected in series between the second or output electrode of mixer H and the control grid 32 of amplifier tube 33, which may be a triode as shown. The amplifier tube functions as the driver stage for a second ampliiier stage 3'4 which is a grounded grid amplifier. The output circuit 36 for the mixer further includes the capacitor 35 which represents the interelec't'rode capacitance between control-grid-SZ and cathode 36 of driver stage 33. The xed tuned resonant output circuit 30 accordingly is av-series-resonant circuit, the resonant frequency of -which may be adjusted by adjustment of inductor 3i as indicated.

A lead or conductor 31 is provided between mixer ii andinductor 3i. This conductor 37 provides inductance and is utilized for picking up an oscillatory wave which is developed by the oscillation generator l2. The oscillation generator l2 may be of any type suitable for developing a U. H. F. wave. Preferably, however, the oscillator is of the type disclosed and claimed in applicants copending application filed on May 29, 1951,",'Serial No. 228,891, entitled Tunable Circuit Structure and assigned to the assignee of this application.

The oscillation generator I2 includes an amplifier tube 38 which may be a triode as shown. The cathode te is` grounded through inductor el, the control grid l2 is grounded through grid leak resistor 43 and the anode i4 is supplied with. a suitable anode voltage indicated at +B through dropping resistor 45 which may be bypassed to ground through bypass capacitor 11E. The lament 4l is supplied with a suitable voltage indicated at -l-E through inductors 5B and ing capacitor 55. In this manner, the oscillation generator may be tuned through a predetermined U. H. F. band. As explained in the Pan application above referred to, the series resonant circuit'52 may consist of a parallel wire transmission line having its open end short-circuited by a Variable capacitor.

The unmodulated carrier wave developed by oscillation generator i2 is now impressed on the conductor or lead 3l. This is efiected by disposing the oscillator i2 or its series resonant circuit 52 is proximity to the conductor 3l so that the oscillatory wave radiated by the series resonant circuit 52 is intercepted by the conductor 3l. It is, of course, to be understood that the oscillatory wave may be impressed in any other suitable manner on the output electrode of crystal mixer' il thereby to reduce oscillator radiation through the antenna It.

An inductor 5S is provided between lead 3l and ground and functions as a choke for the oscillator wave. The'lnductor I56 provdesia treturn path #for the direct current nowing through crystal mixer 1i. 'I'he direct :current flows through lead 3l', inductor 55 and ground and back through inductor and its tap through .crystal -H "The intermediate frequency amplifier :stage I3 which 'may be conventional, wil-l now be Adescribed. The cathode 355 of the driver-"stage 33 isgrounded through a grid bias network 58. A blocking capacitor SE and van inductor `65| yareconn'ected Ain series 'between the control grid 32 and the I'anode t2 4of the vdriver stage 33. `'lheblocking capaci-tor B 'has a knegligible 'impedance at the intermediate frequency. "The 'inductor el neutralizes the capacitor- 63'which indicates the capacitance between anode l32 fand-control grid 32. The anode (i2 is connected tothe anode voltage vsupply +B 4through resistor '64 across which lthe output-signal is developed.

The output signal derived across anode resistor l563 is 'impressed through couplingcapacitor 65 on the cathode t6 of thc-grounded -grid lamplier Bri. Cathode "65 is grounded through inductor El bias network 68 connected in series. l'I'he I cathode lilament lll is connected to a suitable source of filament voltage indicated at -1-E through inductors "Il and 12. Inductor 12 Amay be grounded as vshown and both inductors may be bypassed through bypass capacitor 13.

The anode 'It -of the grounded -grid amplifier stage 3c is connected 'to +B through resistorl and inductor TF5. Re'sistorf'l mayV be bypassed to ground through bypass `'capacitor i. Inductor is tuned by a capacitor v'18 'which `indicates the capacitance between anode 14 and the control grid voi the grounded grid ampl'iier 311. lndu'c'tor Sil is coupled to indu/eter 'l' and the amplified "intermediate 'frequency signal may 'be med-late lreouiency ampliers'ta'ge 113 operates in a conventional manne-r Yand it'isloelieved'that its operation need not be describet-l -detail'here Referring now toFigure .3j-'there fis 'illustrated curve yD326 in dotted lines which `indicates the rectified current Yin `m'illifamperes (lma.) Showing through crystal rectifier 4Il 'in 4response to the impressed oscillatory wave as a function Io'f "fre- Quen'cy. Curve 83 -indicates the operation o'f the .converter of `ligure l vas described rso "afar, .that iis, without equalizing the oscillatory energy in.'accorr`lancewith the'present `invention. will be seen that the rectified current of fthe crystal mixer lli varies over 4a rang-e of approxi-mately 1060 'to l (the rectified crystal'current "-i-s 'plotted on a logarithmic ,.scale). As eXpla'i-nedhere- 'inbefo-re, vthe 'oscillatory energy impressed Uon crystal Ell, which 'is a function of the rectifiedY crystal current, should be maintained Zsubstantially constant overftheituning range lofthe oscillator. Obviously, curve '83 shows vthat the oscillatory I'energy 'fis not constant. n Y

yIn accordance with the present invention, La shunt path S5 is provided as shownby Figure 1 between the output electrode -of lcrystal mixer il and ground. This path -85-=effectively shunts the crystal mixer as shown more clearly in Fig-- ure f2. In the #equivalent circuit 'of Figure 2, the input .electrode -o'f Icrystal mixer -H has been shown grounded. 'Itsl outputelectrode is grounded 'through the `oscillation generator l2 and the coupling circuit '8S including inductor 81, capacitores andresistor `91'! connected in parallel. The parallel resonant-circuit BL-88 represents the inlductive and capacitive coupling ybetween "the d from output terminals El. 'The interc 'e 6 oscillation generator 'l2 :and lcondunrstor .3l while the rresistor f9.6 .indicates the Acoupling resistance. Accordingly, the `path 85 .also :shunts the .equivalent coupling circuit .8e and the roscrllator t2.

In accordance with :the present invention, the shunt path 85 includes a capacitor '92 .and a resistor '93 A"connected vin series between .lead 3l and ground. As illustrated in .Figure 2J `an inductor is furthermore connected in series with capacit'or S2 and resistor '93. The inductor 94 represents the inductance of the leads which connect capacitor 92 and resistor 93 between conductor 37 fand ground.

By way .of example, the resistance of resistor 93 rmay beibetween 27 and .33 ohms .and the .capacitance of :capacitor 59.2 vmay be between .l0

l2 micromicrofarads. The combined impedance of capacitor 92, `resistor 93 land inductor @Il maybe foi the order Aof 30110 ohms and varies over a .range of approximately `l.5 to l over the U. E. F. oscillator tuning range between approximately @L00 yand B00 mc. The solid curve 195 of Figure 3 'indicates the lrectified crystal current as ra vfunction of frequency when the shunt path 85 of the Iinvention is provided. 'Ihe curve j'35 may be adjusted up or down by an adjustment of 'the capacitance of capacitor S2 or by adjusting the coupling between the series resonant circuit 5E of the oscillator yl2 vand conductor 3l.'

The impedance of the shunt path 85 is of the order foi 30 to 4G ohms. This impedance is small compared to the impedance which mixer ll presen-ts to the oscillatory wave and which is of the order of 30D to 400 ohms. The impedance of shunt path 85 is also small compared to the impedance of driver tube 33, which may be of the order of 10G() ohms. The impedance of inductor 5 is valso Vhigh to the oscillatory wave. Accordingly, the impedance of the shunt path d5 determines the oscillatory energy impresse on the mixer Il and maintains this energy substantially constant over vthe tuning range of the oscillator.

The resistor S3 prevents the impedance of the shunt path from becoming aero at the frequency Where inductor gli and capacitor y32 are series resonant. This series resonance may occur within the oscillator tuning range.

The crystal mixer Ii presents an impedance of approximately i ohms to the radioI frequency input `circuit il. This impedance is high corn.- pared to the impedance of the shunt path 85 so that the amount of mismatch between the input circuit l? 'andthe crystal ii is small. On the other hand, at the intermediate frequency the impedance of the shunt path 'S5 is equivalent to a parallel RC circuit having a shunt resistance of the order of 1460 ohms. This equivalent parallel RC circuit is shunted across the crystal mixer i i or'the intermediate 'frequency currents. Since the 'impedancey vof the crystal mixer il to intermediate frequency 'currents vis `approximately 200 ohrns, the shunt path d introduces negligible effecten thematc'hing between the crystal rectiiler il and its intermediate frequency output circuit 39.

There has thus been disclosed a U. H. F. converter wherein the oscillatory energy impressed on 'a crystal mixer is maintained substantially constant throughout the oscillator tuning range. Hence, the optimum oscillatory energy may be impressed on the crystal mixer to improve the noise factor, reduce oscillator radiation and reduce vvspurious responses. This is effected by shunting Ythe crystal 'mixer with a series nctwork consisting of a resistor and a capacitor. The converter of the invention does not require specially constructed elements such as capacitors having substantially no inductance and, therefore, is very inexpensive in production.

What is claimed is:

l.. A U. H. F. converter comprising a crystal mixer having two electrodes, a resonant input circuit tunable within a predetermined portion of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between one of said electrodes and a point of substantially fixed potential, an oscillation generator tunable within another portion of said U. E. spectrum, a resonant output circuit tuned to a predetermined fixed frequency and connected effectively between the other one of said electrodes and said point of xed potential, a conductor providing inductance connected between said other one of said electrodes and said output circuit, means coupling said oscillation generator to said conductor to impress an oscillatory wave thereon, and means for main taining the oscillatory wave energy impressed on said crystal mixer substantially constant throughout the tuning range of said oscillation generator and comprising a capacitor and a resistor connected in series between said other one of said electrodes and said point of xed potential.

2. A U. El. F. converter comprising a crystal mixer having two electrodes, a resonant input circuit tunable within a predetermined portieri` of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between one of said electrodes and a point of substantially fixed potential, an oscillation generator tunable within another portion of said U. El. F. spectrum., a resonant output circuit tuned to predetermined intermediate frequency and connected erectively between the other one of said electrodes and said point of xed potential, a conductor providing inductance connected between other one of said electrodes and said output circuit, said oscillation generator being disposed adjacent to said conductor to impress an oscillatory wave thereon, and means for maintaining the oscillatory wave energy impressed on crystal mixer substan tially constant throughout the tuning range of .said oscillation generator and capacitor, a resistor and an inductive lead con nected in series between said yother one of said electrodes and said point of lxed potential.

3. A U. El. F. converter comprising a crystal mixer having a first and a second electrode, a resonant input circuit tunable over a first portion of the U. il. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between said first electrode and a point of substantially fixed potential, a esonant output circuit tuned to a predetermined fixed frequency and connected effectively between said second electrode and said point of :fixed potential, a conductor providing inductance connected between second electrode and said output circuit, means for impressing an unmodulated carrier wave on said conductor, said unmodulated carrier wave having a frequency variable within a second predetermined portion of said U. H. F. spectrum, and a capacitor and a resistor connected in series between said second electrode and said point of iixed potential, w ereby the ccmbined impedance of said capacitor and resistor Varies within narrow limits over said second precomprising aY determined U. I-I. F. portion and.- effectively shunts the unmodulated carrier wave energy impressed on said crystal mixer to equalize said energy.

4. A U. H. F. converter comp-rising a crystal mixer having a first and a second electrode, a resonant input circuit tunable over a rst portion of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between said first electrode and a point of substantially fixed potential, a resonant output circuit tuned to a predetermined interino diate frequency and connected eiiectively between said second electrode and said point of iixed potential, means for impressing an unmodulated carrier wave on the second electrode of said crystal mixer said unmodulated carrier wave having a frequency variable within a second predetermined portion of said U. H. F. spectrum, a capacitor, a resistor and at least one lead connected in series between said second electrode and said point of fixed potential, said lead providing inductance, whereby the combined impedance of said capacitor, resistor and lead varies within narrow limits over said second predetermined U. H. F. portion and effectively el ents the unmodulated carrier wave energy impressed on said crystal mixer to equalize said energy, said cornbined impedance being small compared to the impedance which said crystal mixer presents to said unmodulated carrier wave.

5. A U. H. F. converter comprising a crystal mixer having a first and a second electrode, a resonant input circuit tunable over a rst portion of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between said rst electrode and a point of substantially xed potential, a resonant output circuit tuned to a predetermined intermediate frequency and connected effectively between said second electrode and said point of xed potential, a conductor providing inductance connected between said second electrode and said output circuit, an oscillation generator disposed adjacent to said conductor for impressing an unmodulated carrier wave thereon, said oscillation generator developing a wave having a frequency variable within a second predetermined portion of said U. H. F. spectrum, a capacitor, a resistor and at least one lead connected in series between said second electrode and said point of xed potential, said lead providing inductance, whereby the com bined impedance of said capacitor, resistor and lead varies within narrow limits over Vsaid second predetermined U. H. F. portion and effectively shunts the unmodulated carrier wave energy impressed on said crystal mixer to equalize said energy.

6. A U. I-I. F. converter comprising a crystal mixer having a first and a second electrode, a resonant input circuit tunable over a first portion of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between said first electrode and a point of substantially fixed potential, a resou nant output circuit tuned to a predetermined intermediate frequency and connected eifectively between said second electrode and said point of fixed potential, means for impressing an unmodulated carrier wave on the second electrode of said crystal mixer, said unmodulated carrier wave having a frequency variable within a second predetermined portion of said U. I-I. F. spectrum, a capacitor and a resistor connected in series between said second electrode and said point of xed potential, whereby the combined impedance of said capacitor and resistor varies within narrow limits over said second predetermined U. H. F. portion and effectively shunts the unmodulated carrier wave energy impressed on said conductor to equalize said energy, said input circuit including a first inductor directly connected between said rst electrode and said point of fixed potential, and a second inductor connected between said conductor and said point of fixed potential, said inductors providing a return path for the direct current flowing through said crystal mixer.

7. A U. H. F. converter comprising a crystal mixer having a first and a second electrode, a resonant input circuit tunable over a first portion of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between said first electrode and a point of substantially fixed potential, a resonant output circuit tuned to a predetermined intermediate frequency and connected effectively between said second electrode and said point of xed potential, a conductor providing inductance connected between said second electrode and said output circuit, means for impressing an unmodulated carrier wave on said conductor, said unmodulated carrier wave having a frequency variable within a second predetermined portion of said U. H. F. spectrum, a capacitor, a resistor and at least one lead connected in series between said second electrode and said point of xed potential, said lead providing inductance, whereby the combined impedance of said capacitor, resistor and lead varies within narrow limits over said second predetermined U. H. F. portion and effectively shunts the unmodulated carrier wave energy impressed on said conductor to equalize said energy, said input circuit including a first inductor directly connected between said first electrode and said point of fixed potential, and a second inductor connected between said conductor and said point of fixed potential, said inductors providing a return path for the direct current flowing through said crystal mixer.

8. A U. H. F. converter comprising a crystal mixer having a iirst and a second electrode, a resonant input circuit tunable over a rst portion of the U. H. F. spectrum to receive a desired modulated carrier wave, said input circuit being connected between said first electrode and a point of substantially fixed potential, a resonant output circuit tuned to a predetermined intermediate frequenoy and connected eiectively between said second electrode and said point of fixed potential, a conductor providing inductance connected between said second electrode Iand said output circuit, an oscillation generator tunable within a second predetermined portion of said U. H. F. spectrum for impressing an unmodulated carrier wave on said conductor, a capacitor, a resistor and at least one lead connected in series between said second electrode and said point of fixed potential, said lead providing inductance, whereby the combined impedance of said capacitor, resistor and lead varies within narrow limits over said second predetermined U. H. F. portion and effectively shunts the unmodulated carrier wave energy impressed on said crystal mixer to equalize said energy, said combined impedance being small compared to the impedance which said crystal mixer presents to said unmodulated carrier wave, said input circuit including a first inductor directly connected between said rst electrode and said point of xed potential, and a second inductor connected between said conductor and said point of fixed potential, said inductors providing a return path for the direct current flowing through said crystal mixer.

WEN YUAN PAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,239,560 Herold Apr. 22, 1941 2,242,791 Ohl May 20, 1941 

